In vivo, vitamin D3 is led to 25-hydroxyvitamin D3 in liver by the hydroxylation of the 25-position and then led to 1α,25-dihydroxyvitamin D3 or 24R,25-dihydroxyvitamin D3 by the hydroxylation of the 1α- or 24-position, respectively. Among those metabolites, for example, 1α,25-dihydroxyvitamin D3 and its synthetic analogues are known to have various physiological activities such as calcium metabolism regulatory activities, growth inhibitory and differentiation inducing activities for tumor cells, and immunoregulatory activities.
Long-term and continuous administration of vitamin D3 has tended to have a disadvantageous effect of causing hypercalcemia. To solve this problem, synthesis of various vitamin D derivatives is discussed and vitamin D derivatives having a reduced hypercalcemic effect have been proposed (e.g., JP No. 7-330714 A and JP No. 10-231284 A).